Conventional fifth-wheel hitch systems involve use of a king pin secured to the underside portion of the forward end of a trailer to be towed, e.g. a camper trailer. The truck used for towing the trailer has a receiver portion mounted to it which is adapted to receive and releasably connect to the king pin. Normally the receiver portion is secured to a framework in the bed of the truck with a plurality of bolts which extend downwardly through the bed and are fastened to the truck frame. The receiver portion (a receiver plate) may be attached to the hitch framework by means of a yoke member which allows the receiver plate to tilt or rotate about a horizontal plane which is perpendicular to the longitudinal axis of the truck. This feature allows the receiver plate to tilt forwardly or rearwardly, for example, relative to the hitch framework when the towing truck goes over inclines or sloping terrain where the rear wheels of the truck become raised (or lowered) relative to the front of the truck.
However, in certain towing situations the trailer is subjected to various twisting forces, e.g. when the towing vehicle is tipped to one side or the other relative to the trailer, such as when the towing vehicle turns onto or off from a roadway which is lower or higher than its current path. In those situations one side of the towing vehicle becomes higher that the other side while the trailer is still in the original plane. This twisting action also can occur when only one side of the towing vehicle travels over a bump (or through a hole). These twisting forces are very undesirable. They place further burdens on the hitch system itself, and the trailer frame can be twisted or otherwise damaged.
A prior art method for alleviating the problem of twisting forces in the fifth-wheel hitch involves the use of a universal joint in which there are two axis of rotation at 90° to each other. This necessarily requires maintenance of two joints and also adds to the overall weight and cost of the hitch system.
There has not heretofore been provided a fifth-wheel hitch system having the advantages and features of the present invention.